For nearly as long as there have been wheeled vehicles, there have been hitch structures to enable one vehicle to pull a trailer or other similar towed load. While such hitch structures have been tried in many shapes, the most popular shape is a ball hitch, wherein the towing force is transferred from the towing vehicle to the towed load using the exterior surface of a generally spherical ball. A coupler on the towed load has a hollow cup shape that fits over and engages the ball. By using a ball hitch, the towed load can be pulled at a wide range of angles and elevations relative to the towing vehicle, for towing over undulating and curving roads and travel paths.
With ball hitches being very popular types of hitches, numerous different arrangements have been designed to enable quick interchanging of the hitch ball. In many instances, the sole purpose of interchangeability is to allow a quick change from a ball of one diameter to a ball of a second, different diameter. Such interchangeable ball hitches may have a post secured to the towing vehicle, with the post configured to engage any of several different diameter balls. In other cases, a separate purpose of interchangeability is to enable substantially complete removeability of the ball hitch from the towing vehicle, so non-towing use of the vehicle is not obstructed by the ball hitch. For either or both purposes, the interchangeable hitch ball should be rugged and securely attachable so as to minimize or eliminate the possibility of unintended disengagement of the ball.
One example of an interchangeable hitch ball is provided in U.S. Pat. No. 4,201,400 to Hoogenbosch. The Hoogenbosch ball hitch sits on a shank, and includes a plunger which is movable up and down within the hitch ball. In the towing position, an enlarged portion of the plunger pushes two balls out of a transverse bore in the shank. When the user wants to remove the hitch ball, the user depresses the plunger so the enlarged portion is no longer in contact with the balls, so the balls can retreat into the shank and the shank can be removed from its collar on the towed vehicle. While the Hoogenbosch device permits a quick and easy removal of the hitch ball, depressing of the plunger to accomplish removal creates its own potential problems. Namely, there is a possibility that the plunger could depress during use of the hitch, such as by debris left in the hitch cup of the coupler. Better solutions which avoid such failure possibilities are needed.
The interchangeable hitches disclosed in Belinky and Belinky et al., U.S. Pat. Nos. 6,616,168 and 8,011,685, borrow from the concept of Hoogenbosch, but move the plunger in the opposite direction. Namely, in the Belinky designs the plunger is moved upward rather than depressed. In the Belinky '168 patent case, the plunger is threaded into the hitch ball. In the Belinky '685 patent case, the plunger is pulled upward against a spring. Because removal of the hitch ball requires the plunger to be moved upward above the profile of the spherical ball, the hitch ball is prevented from inadvertent disengagement whenever the coupler is over the hitch ball. However, the Belinky designs are cumbersome to engage and disengage into the sleeve. In the Belinky '168 patent case, the plunger must be rotated numerous revolutions using a tool such as an Allen wrench to sufficiently move the plunger upward or downward for disengagement or engagement. In the Belinky '685 patent case, no tools are required, but the plunger must be held upward against the spring force for the balls to retract. Holding the plunger upward is difficult to do while dropping the hitch ball into the sleeve.
Hord et al., U.S. Pat. Pub. No. 2005/0104326 operates much like Belinky '685, but the plunger operates two cam members rather than two balls. In the Hord case, the spring pushes the plunger upward, so it always disengages whenever the coupler is not present. This in turn gives the user no way to test and ensure that the hitch ball is secured prior to having the coupler in place.
While Hoogenbosch, Belinky, Belinky et al. and Hord et al. have all come up with forms of solutions that enable the hitch ball to be fully removed from an underlying sleeve, more improvements are possible and needed.